A jar contains $5$ red marbles, $8$ green marbles, and $10$ blue marbles. If a marble is randomly chosen, what is the probability that it is not green?
Answer: There are $5 + 8 + 10 = 23$ marbles in the jar. There are $8$ green marbles. That means $23 - 8 = 15$ are not green. The probability is $ \frac{15}{23}$.